1. Field of the Invention:
The present invention relates to a device for the electro-optical display of the tuning of a television and/or sound radio receiver, and more particularly to such a device having a circuit for directly or indirectly measuring the tuned frequency received, and to an electro-optical display instrument.
2. Discussion of the Prior Art:
When tuning a television and/or sound radio receiver to a particular transmitter, the resonant frequency of at least the input circuit of the receiver is adjusted to the frequency of this transmitter. This can be accomplished directly by mechanically rotating or displacing parts of a tuning capacitor or of an inductor, or indirectly by changing the control voltage on an electrically controlled tuning element. For an optical display of the tuning of the receiver, it is customary to transfer the rotation or displacement of the capacitor or inductor, or of the voltage source for the tuning element in the input circuit, by means of a mechanical coupling mechanism to a pointer which is located, rotatably or displaceably, in front of or behind a graduated or inscribed scale.
This customary display device has several disadvantages. The synchronization between the rotation or displacement of the tuning device or the voltage source and that of the pointer is inaccurate, and this is found to be troublesome, particularly in the case of high frequencies. For this reason, it is virtually impossible, even with very precise display devices of this type, to tune accurately to a transmitter solely with the aid of the frequencies or wavelengths plotted on the graduated scale. Moreover, because of the frequency-dependent "spacing" of the transmitters, it is not possible to distribute the names of the transmitters uniformly on the surface of the scale and, for this reason, the names of transmitters indicated on the scale usually coincide only partially with the transmitters which can in fact be received. Finally, these display devices with their multiplicity of mechanically moving parts are relatively involved and correspondingly expensive and require much space, which is inapposite to the electronics of the receiver, which is increasingly miniaturized and constructed without moving parts.
Various electronic display devices, by means of which the disadvantages described are to be overcome, have therefore already been disclosed.
In a first known display device (Funk-Technik, 1971, No. 5, page 157 et seq.), the frequency received is displayed by means of digital display elements. For this purpose, the oscillations of the heterodyne oscillator, the frequency of which is in a defined ratio to the resonant frequency of the input circuit, are converted to pulses, the pulse frequency is stepped down and the pulses are then passed periodically to a counter during a preset period of time. With an appropriately corrected counter, the number of the pulse counted can be displayed directly as the frequency received.
In another known display device (DT-OS 2,435,088), the tuned frequency received is displayed in a quasi-analog manner with the aid of display elements arranged in the form of a band. To operate this device, the control voltage for an electrically controlled tuning element is converted in an analog digital converter into a pulse train, the pulse frequency is counted and the signals appearing at the output of the counter are passed to a decoder, the outputs of which are each connected to one of the display elements arranged in the form of a band and which excites a display element corresponding to the counted pulse frequency.
These two known electro-optical display devices have no mechanically moving parts and at least the first-mentioned device makes it possible to display the tuned frequency received very accurately. Both devices have, however, the disadvantage that they only display the tuned frequency received, and therefore it is not possible to see whether this tuned frequency corresponds to a desired transmitter station or to a transmitter station name. In the first-mentioned device, in order to associate the display frequency to a transmitter, it is necessary to use an additional conversion table or chart. The second quasi-analog display device can be combined with a scale of the type hitherto customary, but even then, at least the problem of distributing the station names on the surface of the scale remains.